The present invention relates to the field of optically readable and recordable information carrier disks, whereby the information is recorded in the form of a two level relief modulation translating a frequency-modulated video signal or videodisk, an audio-modulated signal or audiodisk or binary signals when such a carrier is used as an information memory.
The invention more specifically relates to a semiconductor laser source optical reading head incorporating a reduced number of elements to form an optical head having low weight, small size and low cost. The invention also relates to an optical recording and/or reading device incorporating such an optical head.
In the laser source optical heads presently used for recording or reading information carrier disks, the laser source is placed on the axis of the optical reading or recording system and lights up the entrance pupil of the optical system in a symmetrical manner with respect to the axis, both in the direction y, tangential to the track carried by the carrier and in the radial direction, x, orthogonal to y in the plane of the support. In an optical device for reading by reflection and incorporating such an optical head, the reading signal and the vertical and radial variation signals result from the radiation reflected by the disk, so that it is necessary to provide supplementary optical elements for separating the reflected radiation from the incident radiation. Conventionally, this separation is obtained by successively placing on the optical axis a separating cube utilizing birefringence as a function of the polarizations of the radiation which it receives and a quarterwave plate. As the laser source is polarized in a linear manner, the radiation reflected by the support traverseing the quarter-wave plate has a polarization displaced by .pi./2 relative to that of the radiation from the source and this radiation is deflected by the cube. Such an optical head has a large number of cooperating members constituting a cumbersome assembly, with a relatively high cost and whose weight is too high to enable such a head to be radially moved rapidly.